Dynamic UI second filter not changing data

[Nick1991]

I am trying to make an application with 2 filters.
The first filter gives choices of coloumn name.
The second filter gives choices of rows from the selected coloumn.
I have managed to use uiOutput and renderUI to make the second filter dynamic BUT...
The data doesnt reflect the selection of the second filter.

cars<-mtcars[8:11]
library(shiny)
ui <- fluidPage(
selectInput("a","selection1",names(cars)),
uiOutput("b"),
tableOutput("x")
)

server <- function(input, output, session) {
output$b <- renderUI({

selectInput("b", "selection 2", choices =  unique(cars[,input$a]))

})
r<-reactive({
s<-cars[input$a,input$b]
})

output$x<-renderTable({r()})
}

shinyApp(ui, server)

*NOTE: I am still unfamiliar with observe and isloate function.

[nirgrahamuk]

if input$a represents the column choice, and input$b the row choice, the proper order when using square brackets to subset a data.frame is rows first then columns. compare

> mtcars["vs",1:3]
   mpg cyl disp
NA  NA  NA   NA

> mtcars[1:3,"vs"]
[1] 0 0 1

[nirgrahamuk]

if you want your result of such a subset to always be in data.frame/tibble form then best make cars be a tibble, otherwise as you see, selection of a single column, would cause the return to be the raw vector unwrapped from the containing frame

[Nick1991]

My second dynamically created filter has the correct options but does not change the data.

[nirgrahamuk]

library(shiny)
library(tidyverse)
cars<-tibble(mtcars[8:11])
ui <- fluidPage(
  checkboxInput("fullrowtoggle","show full rows ?",value=TRUE),
  selectInput("a","selection1",names(cars)),
  uiOutput("b"),
  tableOutput("x")
)

server <- function(input, output, session) {
  output$b <- renderUI({
    
    selectInput("b", "selection 2", choices =  unique(cars[,input$a]))
  })
  r<-reactive({
    s<- cars |> filter(!!sym(req(input$a)) %in% req(input$b))
    if(isTruthy(input$fullrowtoggle))
      return(s)
    s |> select(any_of(input$a))
  })
  
  output$x<-renderTable({r()})
}

shinyApp(ui, server)